1. Field of the Invention
The present invention relates to a method and an apparatus for thermal printing on a large printing area such as a surface of cardboard, wood, or concrete constituting a part of a box or a container.
2. Description of the Background Art
In general, as a method of printing a limited number of patterns onto a large number of objects uninterruptedly, there is known a method using a stamp.
On the other hand, conventionally, a thermal printing has been utilized in printing on a small printing area, in which the printing is achieved by placing a carbon ribbon over a printing surface and moving a printing head over the carbon ribbon to thermally print desired patterns on the printing surface.
Such a conventional method of thermal printing is known to be associated with the following drawbacks, which has severely limited a practical implementation of an apparatus for thermal printing as well as its fields of applicability.
First of all, the conventional thermal printing is primarily concerned with a printing of a small printing area at a given printing position, so that when such a conventional thermal printing is applied for a printing of diverse patterns on a large area such as a printing of bar codes on a cardboard box, a large size printing apparatus was necessary and a cost of printing increased inevitably.
Secondly, in a conventional thermal printing apparatus, it has structurally not been possible to print patterns with a part of patterns left blank which is to be printed at later time by means of handy type printer for example.
Thirdly, in a conventional apparatus for thermal printing, the imprinting of patterns on the carbon ribbon by the printing head and the thermal printing of the patterns from the carbon ribbon to the printing surface take place at the same position, so that a stability of the printing head with respect to the printing surface is a crucial factor for an accurate printing. Now, in printing a large printing surface such as a cardboard, the printing head has conventionally been supported by a bridge structure bridging over the printing surface. However, such a bridge structure is known to be not stable enough to obtain a sufficient stability for the thermal printing of patterns requiring a high accuracy such as bar codes.